A control valve for a variable displacement compressor that is used to compress the refrigerant of an automobile air conditioning device is known as an example of a control valve having a pressure sensing section that applies an urging force to a movement member according to a pressure introduced to the pressure sensing section, wherein the movement member is moved by the urging force to adjust the degree of valve opening (see Patent Document 1). This control valve uses a bellows assembly in the pressure sensing section, and FIG. 5 is a schematic sectional view showing this type of control valve for a variable displacement compressor.
As shown in FIG. 5, the control valve 1 is composed of a solenoid section 2, a valve section 3, and a bellows assembly 4. The solenoid section 2 is disposed at one end of a cylindrical valve body 5, magnetic force is generated by applying an electrical current to a coil 6, a movable iron core 7 is moved against a spring 8 toward a fixed iron core 9 disposed to the left, and an urging force proportional to the square of the current value is applied to a valve rod 10. A port 11 communicated with the region of the discharge pressure Pd of the variable displacement compressor, and a port 12 communicated with an inner chamber (chamber pressure Pc) of the variable displacement compressor, are formed in the valve body 5; and the valve section 3 is configured so as to be capable of adjusting the rate of flow of discharged refrigerant gas into the inside of the compressor on the basis of the degree of opening of a valve element 13 formed at an end of the valve rod 10 with respect to a valve seat 14.
At the other end of the valve body 5 from the solenoid section 2, the bellows assembly 4 is provided to a pressure sensing chamber 16 composed of a case 15 and the valve body 5, and suction pressure Ps of the compressor acts on the pressure sensing chamber 16. The bellows assembly 4 has a bellows 19 that is retained at both ends by holders 17, 18 so as to be able to expand and contract, a spring 20 extends between the holders, and a connecting rod 21 in contact with and connected to both members is disposed between the holder 18 and the left end 10a of the valve rod 10. Consequently, the bellows 19 is expanded and contracted by the change in the suction pressure Ps introduced to the pressure sensing chamber 16, the urging force applied to the valve rod 10 changes, and the degree of valve opening is made variable.
The balance of forces acting on the valve rod 10 when the control valve 1 thus configured is open is indicated by the equation Ps=(F1+F2−F)/A, wherein F1 is the urging force of the spring 20, F2 is the urging force of the spring 8, F is the solenoid thrust, and A is the effective pressure surface area of the bellows. As is also apparent from this equation, since the suction pressure Ps achieves balance at a low value when the solenoid thrust F is increased, and the suction pressure Ps achieves balance at a high value when the solenoid thrust is reduced, the control valve is highly useful as a control valve for a variable displacement compressor used to compress the refrigerant of an air conditioning device.
Patent Document 1: Japanese Laid-open Patent Application No. 2001-141086 (paragraphs 0015 through 0018, and FIGS. 1 and 4)